Large Intestine

Large Intestine

The large intestine reabsorbs the water from indigestible food material and processes the waste material (Figure). The human large intestine is much smaller in length compared to the small intestine but larger in diameter. It has three parts: the cecum, the colon, and the rectum. The cecum joins the ileum to the colon and is the receiving pouch for the waste matter. The colon is home to many bacteria or “intestinal flora” that aids in the digestive processes. The colon has four regions: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The main functions of the colon are to extract the water and mineral salts from undigested food and to store waste material.

Illustration shows the structure of the large intestine, which begins with the ascending colon. Below the ascending colon is the cecum. The vermiform appendix is a small projection at the bottom of the cecum. The ascending colon travels up the right side of the body, then turns into the transverse colon. On the left side of the body the large intestine turns again, into the descending colon. At the bottom, the descending colon curves up; this part of the intestine is called the sigmoid colon. The sigmoid colon empties into the rectum. The rectum travels straight down, to the anus.
The large intestine reabsorbs water from undigested food and stores waste until it is eliminated. (credit: modification of work by Mariana Ruiz Villareal)

The rectum (Figure) stores feces until defecation. The feces are propelled using peristaltic movements during elimination. The anus is an opening at the far-end of the digestive tract and is the exit point for the waste material. Two sphincters regulate the exit of feces; the inner sphincter is involuntary, and the outer sphincter is voluntary.